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Файл:Basics of Physics II (Основы физики II). Учебное пособие
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b) distinct, solid, seemingly;
c) predict, evidence, proper;
12. Which topics are not discussed in the text:
a) the definition of light
b) properties of a wave
c) properties of a particle
d) the reason of particle-wave dualism of light
e) the proof of particle-wave dualism of light
f) the distinction between a wave and a particle
g) the double slit experiment
13. Formulate the main idea 1) of the whole text; 2) of each paragraph.
14. Answer the questions:
1) What problem did light pose?
2) What became necessary to explain the behaviour of objects on the smallest scale?
3) What is a particle from classical point of view?
4) How is the motion of a classical particle governed?
5) What is a wave from classical point of view?
6) What do Maxwell’s equations predict?
7) What is light eventually? How is it proved?
8) How such contradictory properties as a wave and a particle can be reconciled?
15. Match beginnings and endings of the sentences:
1) The details of the photoelectric effect were
in direct
a) no matter what the intensity.
2) Increasing the intensity of the light increased
b) proportional to the frequency of the illuminating light.
3) Red light will not cause the ejection of electrons,
c) contradiction to the expectations of very
well developed classical physics.
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4) A weak violet light will eject only a few
electrons, but their maximum kinetic energies
d) you will find that their DeBroglie wavelengths are ridiculously small.
5) The electrons were emitted immediately -
e) the circumference of an electron orbit in
such a way as to experience constructive interference.
6) Analysis of data from the photoelectric experiment showed that the energy of the ejected
electrons was
f) no time lag.
7) So it might be implied that there must be a
particle treatment of refraction of light,
g) the number of photoelectrons, but not their
maximum kinetic energy.
8) In the Bohr model of atomic energy levels,
the electron waves can be visualized as "wrapping around"
h) to the transmission plane is selectively absorbed.
9) If you explore the wavelength values for ordinary macroscopic objects like baseballs,
i) are greater than those for intense light of
longer wavelengths.
10) In dichroic materials like polaroid, the
component of the field perpendicular
j) but for ordinary optics the wave view of light
is the practical approach.
16. Read the following text carefully and fill in the gaps (you should use only one word in each
gap):
Here are some more details on the ways each classical model fails for light:
1. Light is not a (1)___________ wave. For example, consider the photoelectric (2)___________
using a “dust cathode.” When light of low intensity is shown on fine metallic dust, photo-electrons
start coming off immediately, whereas wave (3)___________ predicts that a long time must elapse
before a dust particle can collect (4)___________ energy over its area from a wave to emit a photoelectron.
2. Light is not a (5)___________ particle. That is, the photon cannot be thought of as having a
straight-line (6)___________ of infinitesimal width. Experiments designed to establish which part
of the slit opening a given (7)___________ crossed (for example by having a second, narrower slit
will cause a further diffraction or other disturbance of the photon and no definite path can be established. It is most correct to (8)___________ of photons only at their instant of creation or destruction, and to consider light to (9)___________ a probability wave in between these times, although
in the geometrical limit (resolution of the path is less than √𝐿𝜆) an approximate trajectory can be
assigned to the light wave, as though it were a (10)___________.
WRITING
17. Write a scientific definition of a photon taking into consideration its wave-particle duality.
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SPEAKING
18. Search for necessary information and prepare for oral reports:
a) the double slit experiment;
b) light is a particle — history of discovery;
c) light is a wave — history of discovery;
d) the ‘measurement problem’ of quantum physics.
19. Extended discussion:
Apart from models of light described in the article some scientists also mention a ray model of
light.
A light ray will be reflected from a smooth surface in such a manner that the angle incident
ray makes normal to the reflecting surface at the point of incidence which is precisely equal to
the angle that the reflected ray makes with normal. Also, the reflected ray along with the incident
ray and the normal to the reflecting surface all lie on the same plane defined at the incident point.
The optical ability of humans and other animals is the consequence of the complex interaction of light, eyes and brain. People are able to see because light from an object can move through
space and influence our eyes. When light reaches our eyes, signals are sent to our gray matter, and
our brain deciphers the information in order to perceive the appearance, location and movement
of the objects we are looking at. If a ray of light could be witnessed approaching and reflecting off
of a flat mirror, then the manner of the lights reflection would follow a predictable law known as
the law of reflection.
The ray model is extremely useful while studying reflection of light, refraction of light and
various images created by lenses, spherical mirrors and plane mirrors.
How can all three models be used at the same time? Why do they not exclude each other? What are
their applications? Discuss in
small groups, then summarize
your ideas and present to the
whole class as a short statement.
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20. Challenge questions — test yourself!
1) Which of the following is true about light?
I) It is an electromagnetic wave
II) It does not propagate in vacuum
III) Its maximum speed is approximately 3×108 m/s
A) I only
B) I and II only
C) I and III only
D) III only
E) I, II and III
2) The speed of light in a certain material is 50% of its speed in vacuum. What is the refractive index of this material?
A) 1.5
B) 0.5
C) 6.0
D) 2.0
E) 1.5×10
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3) What is the critical angle ic at the interface glass-cladding of an optical fiber whose core has a refractive index equal to 1.5 and cladding with a refractive index 1.45?
A) 15°
B) 105°
C) 86°
D) 83°
E) 75°
4) Which of the following is true about light with a single wavelength?
I) It can be refracted
II) It cannot be dispersed
III) It can be reflected
A) I, II and III
B) I and II only
C) II and III only
D) I and III only
E) None
LISTENING
21. You are going to watch a video named Is Light a Particle or a Wave? Before you start,
read the next words from this video and make sure you understand their meanings:
to originate, vision, a probe, intelligence (information), a lightbulb, chalk, a ripple, a still pond
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22. Watch the video and choose if the following statements are true or false:
1) Ancient Greeks gave the first scientific explanation of the phenomenon of light.
2) According to ancient Greeks, light originated in our eyes.
3) Only 100 years later this idea was disproved.
4) Alhazen’s theory was good but couldn’t explain why it gets dark.
5) Newton assumed light to be made of tiny atom-like particles which he called quanta.
6) After Newton’s death scientists experimentally proved that light isn’t made of small atom-like
particles.
7) Two crossing beams of light interact with each other.
8) Interference patterns happen when two waves occupy the same space.
9) Particles never make interference patterns unlike waves.
10) Light is both a wave and a particle at the same time.
23. Watch the video once more and complete the tasks:
1) Shortly explain ancient Greeks’ theory about light.
2) Shortly explain Alhazen’s theory: what ideas different from earlier ones did he suggest?
3) What was Isaak Newton’s theory of light? What was wrong with it?
4) Eventually what is light?
24. DEVICE EXPLANATION
Using the facts below and the scheme of the device, explain the work of the interferometer:
✓ its structure;
✓ its purpose;
✓ how do you use it.
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About the device
An interferometer is a really precise scientific instrument designed to
measure things with extraordinary accuracy. The basic idea of interferometry involves taking a beam of light (or another type of electromagnetic radiation) and splitting it into two equal halves using what's
called a beam-splitter (also called a half-transparent mirror or halfmirror). This is simply a piece of glass whose surface is very thinly
coated with silver. If you shine light at it, half the light passes straight
through and half of it reflects back—so the beam-splitter is like a
cross between an ordinary piece of glass and a mirror.
Working mechanism
One of the beams (known as the reference beam) shines onto a mirror
and from there to a screen, camera, or other detector. The other beam
shines at or through something you want to measure, onto a second
mirror, back through the beam splitter, and onto the same screen. This
second beam travels an extra distance (or in some other slightly different way) to the first beam, so it gets slightly out of step (out of
phase). When the two light beams meet up at the screen, they overlap
and interfere, and the phase difference between them creates a pattern
of light and dark areas (in other words, a set of interference fringes).
The light areas are places where the two beams have added together
(constructively) and become brighter; the dark areas are places where
the beams have subtracted from one another (destructively). The exact
pattern of interference depends on the different way or the extra distance that one of the beams has traveled. By inspecting and measuring
the fringes, you can calculate this with great accuracy—and that gives
you an exact measurement of whatever it is you're trying to find.
Tips
• Interferometers are widely used in all kinds of scientific and engi-
neering applications for making precise measurements. By scanning interferometers over objects, you can also make very detailed
maps of surfaces.
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• Astronomers also use interferometers to combine signals from tel-
escopes so they work in the same way as larger and much more
powerful instruments that can penetrate deeper into space.
• Interferometry is also helping us to figure out the secrets of grav-
ity.
Warning
A state-of-the-art interferometer can measure distances to within 1 nanometer (one billionth of a meter, which is about the width of 10 hydrogen atoms), but like any other kind of measurement, it's subject to
errors. The biggest source of error is likely to come from changes in
the wavelength of the laser light, which depends on the refractive index of the material through which it's traveling. The temperature,
pressure, humidity, and concentration of different gases in the air all
change its refractive index, altering the wavelength of the laser light
passing through it and potentially introducing measurement errors.
TRANSLATION
25. Translate the text from English into Russian:
A misconception which most physicists acquire in their formative years is that the photoelectric
effect requires the quantization of the electromagnetic field for its explanation. The following quotation taken from a widely used physics text book' illustrates the point.
"Einstein's photoelectric equation played an enormous part in the development of the modern
quantum theory. But in spite of its generality and of the many successful applications that have been
made of it in physical theories, the equation ℎ𝜈 = 𝐸 + ∅ is, as we shall see presently, based on a
concept of radiation - the concept of 'light quanta! - completely at variance with the most fundamental
concepts of the classical electromagnetic theory of radiation".
In fact we shall see that the photoelectric effect may be completely explained without invoking
the concept of "light quanta". To be sure, certain aspects of nature require quantization of the electromagnetic field for their explanation, for example:
1. Planck distribution law for black body radiation (1900);
2. Compton effect (1926);
3. Spontaneous emission (Dirac, 1927);
4. Electrodynamic level shifts (1947).
The photoelectric effect is definitely not included in the foregoing list. It is an historical accident
that the photon concept should have acquired its strongest early support from Einstein's considerations on the photoelectric effect.
26. Translate from Russian into English:
Эффект Комптона и фотоэффект подтверждает корпускулярную природу света. Свет ведет себя как поток частиц – фотонов. Тогда как же частица может обнаруживать свойства,
присущие классическим волнам? Ведь частица может пройти либо через одну, либо через
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другую щель. Однако известна интерференция света от двух щелей (опыт Юнга). Таким образом, мы пришли к парадоксу – свет обладает одновременно и свойствами корпускул, и свойствами волн. Поэтому говорят, что свету свойствен корпускулярно-волновой дуализм.
Противопоставление квантовых и волновых свойств света друг другу является ошибочным. Свойства непрерывности электромагнитного поля световой волны не исключают свойств
дискретности, характерных для световых квантов – фотонов. Свет одновременно обладает
свойствами непрерывных электромагнитных волн и свойствами дискретных фотонов. Он
представляет собой диалектическое единство этих свойств. С уменьшением длины волны все
более отчетливо проявляются квантовые свойства света (с этим связано, например, существование красной границы фотоэффекта). Волновые же свойства у коротковолнового излучения
проявляются весьма слабо (например, дифракция у рентгеновских лучей). У длинноволнового
же излучения квантовые свойства проявляются слабо и основную роль играют волновые свойства.
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PART 3
Images
No lens is quick enough to track the movement of the human body.
The molecules are always moving.
Roger Rees
LEAD-IN
1. Answer the following questions:
1) What is an image?
2) How does an image form?
3) What is a lens used for?
4) How many types of lenses are there? Can you name them all?
PRE-READING
2. Match the word with its definition:
1) a convex lens
a) the distance from the center of the lens to
the point where it focuses light rays
2) a concave lens
b) a type of lenses which surface bulges inwards in the centre
3) a focal point
c) an optically formed reproduction of an object
4) a focal length
d) a crystalline body whose lateral faces meet
at edges that are parallel to each other
5) a reflexive index
e) a surface that forms the boundary between
two bodies, liquids, or chemical phases
6) a prism
f) a type of lenses which surface bulges outwards in the centre
7) an image
g) the place to which rays of light converge or
from which they appear to diverge after refraction or reflection
8) an interface
h) the speed of light in a vacuum divided by
the speed of light in the substance in question
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READING
3. Look at the headings from the text Lenses. Can you answer any of these questions before
reading the text? Try to answer them in pairs.
What are lenses?
How are lenses made?
What are lenses used for?
4. Now read the text and check if your answer is close to its information, then insert the words
at the end of this text into spaces (1 - 13):
Lenses
Microscopes let us peer inside invisible worlds our eyes could never see, telescopes take us far
(1)__________ the Earth to the stars and planets of the night sky, movie projectors throw enormous
images onto screens, and lighthouses cast reassuring beams of light far across the ocean. Amazing
curves of glass or plastic called lenses make all these things possible.
What are lenses?
A lens is a transparent piece of glass or plastic with at least one curved surface. It gets its name
from the Latin word for "(2)__________" (a type of pulse used in cooking), but don't let that confuse
you. There's no real reason for this other than that the most common kind of lens (called a
(3)__________ lens) looks very much like a lentil!
How are lenses made?
Until plastics became common in the 20th century, (4)__________ all lenses were made by
grinding solid pieces of glass into different shapes. Convex lenses were made by using a
(5)__________-shaped grinding tool (and vice-versa), and then the roughly shaped lens was polished
to make its final shape. The ordinary glass we use in windows and crockery isn't good enough to use
for lenses, (A) ____ it contains air bubbles and other imperfections. These cause (6)__________ to
divert from their correct path, making a fuzzy image or one that makes different colors of light behave
in different ways (problems that optical scientists refer to as aberrations). (B) ____, lenses are made
using a more refined material known as optical glass. For eyeglasses, many people now prefer plastic
lenses because they're much lighter and safer than optical glass. Plastic lenses can be (7)__________
to shape, instead of being ground, (C) ____ they can be made in huge quantities far more cheaply
than glass lenses. (D) ____ ordinary plastic scratches easily, it can be (8)__________ with a thin
layer of a protective material such as diamond-like carbon (DLC) to reduce the risk of damage. Some
optical lenses are also coated with thin plastic to reduce annoying reflections.
What are lenses used for?
Lenses are everywhere in the world around us—in everything from car (9)__________ and
flashlights to the LED lights used in electronic instrument panels.
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